Electromagnetic coupling circuits have been used for many years for transferring torque between two rotatable members and for providing a medium for transferring an electrical signal between a rotary member and a fixed member.
Generally, such coupling circuits comprise a magnetic stator member that includes electrical windings that upon electrification create an electromagnetic field whose force is operative to either attract or repel a rotor member according to the direction of current flow through the windings. Such is commonly employed in magnetic clutches and the like where one part of a frictional clutch member is either biased into or away from engagement with a second part of the clutch member and electrification of a magnetic portion of one of the parts is operative to overcome the bias and either engage or disengage the parts.
More particularly, electromagnetic coupling circuits are advantageous for transferring an electrical signal from a stationary member to a rotary member or vice versa. In such cases, the rotor carries electrical windings into which is induced an electrical current as the rotor windings enclose lines of magnetic flux created by the electromagnetic field created by the stator windings so that by means of such electromagnetic coupling circuits an electrical signal such as voltage can be transferred from the fixed to the rotary member or vice versa.
Such electromagnetic coupling circuits are particularly advantageous for rotary transducers operative to monitor stress imposed upon a rotating shaft such as disclosed in U.S. Pat. No. 4,610,168, owned by the assignee of the present and the disclosure of which is incorporated herein by reference. Such transducers commonly employ two electromagnetic stator-rotor assemblies at opposite ends of a section of a rotating shaft that has been altered in some manner such as by having a reduced diameter or having flats dressed onto its outer surface to provide an enhanced stress monitoring section.
A sensor such as a RTD or piezo-electric, or piezo resistive or acoustic emission transducer, or resistance or capacitive strain gage is secured to the enhanced section as part of the sensing circuit to which an excitation voltage or signal is delivered by means of one of the coupling circuits and whose output signal corresponding to stress is transferred from the rotary to the fixed member for processing by mean of the other coupling circuit.
Wheatstone bridges are commonly employed in such circuits and may be located either on the rotary or the fixed member such as, for example, where both a resistance strain gage and its associated wheatstone bridge are both secured to the enhanced stress monitoring section of the rotary member.
Up until the time of the present invention, a problem has existed in providing electromagnetic coupling circuits for large diameter rotary shafts. Such shafts necessarily require correspondly large diameter rotors which require large diameter magnetic stators for providing effective electromagnetic coupling.
Such large magnetic stators may be six or more inches in diameter and are extremely difficult and costly to make in one piece. They are commonly made by molding or machining ferromagnetic material such as an iron-based composition which is then secured to a support member which is secured to and electrically insulated from the fixed member.
The present invention overcomes the difficulties and expense associated with large diameter magnetic stators heretofor used by breaking completely away from past practice and providing an electromagnetic coupling circuit operative over a broad range of rotor and stator diameters by providing a magnetic stator of the type hereinbefore described that comprises a plurality of wedge shaped sections spaced circumferentially about the rotary member that are substantially less difficult and costly to make than the one-piece magnetic stators hereinbefore employed.